System and method for providing a time varying gain TDR to display abnormalities of a communication cable or the like

ABSTRACT

In a system and method for testing and displaying the abnormalities, includes opens, shorts, bridged-taps and wet sections, of a copper pair line for xDSL service use, the abnormalities are amplified and normalized so as to be displayed within a predetermined observation range. The normalization steps include piecewise gaining and biasing the reflected pulse of various gains to create a first normalized reflected trace which match the reflected traces within a predetermined observation range and thereby constitute a total smooth curve; and amplifying the first normalized reflected trace according to a function of time to create a second normalized reflected trace so as to eliminate an exponential gain decay curve of a no-fault copper pair line with the same predetermined characteristic parameters from the first normalized reflected trace to thereby obtain a second normalized reflected trace showing any amplified abnormalities.

BACKGROUND OF THE INVENTION

[0001] A. Field of the Invention

[0002] The present invention related to a system and method forproviding a time varying gain TDR to display abnormalities in acommunication and telephone cable or the like by normalizing the levelsof the reflected signals corresponding to a predetermined observationrange. The communication cable can be any copper pair line that can beused for IDSL, ADSL, HDSL, SDSL, SHDSL, and VDSL communication usage, aswell as all other DSL-type technologies (hereinafter, “xDSL” indicatingall the various DSL technologies and line codings).

[0003] B. Description of the Prior Art

[0004] Internet access providers, cable communication companies, etc.are constantly working to fill demands for real-time internet accessthrough the installation of fiber-optic and other hi-speedcommunications lines. However, in many areas of the country, suchequipment and the services to support that equipment are eitherimpractical to implement, prohibitively costly, or simply not scheduledto occur in the foreseeable future.

[0005] Telephone companies have tried to fill part of the demand byoffering Digital Subscriber Line (xDSL) services that use the currentinfrastructure of copper pair lines to deliver hi-speed access to theInternet. Lines that work fine for standard telephone communication donot always work for different types of DSL operation.

[0006] The definition of copper pair lines includes any communicationline made of copper or other similar material or composition known inthe art. The proper conditions have to exist in order for a copper pairline to handle xDSL communications. The efficiency of a copper pair linefor xDSL service is dependent on factors such as the length of thetelephone line, the number of bridge taps on the line, material defectsor shorts in the line, the wire gauge of the line, damage to the lines,proximity of sources of electromagnetic energy, etc.

[0007] Time Domain Reflectometers or TDRs are in common use in testingthe abnormality of telephone and coaxial cables, such the TDR describedin U.S. Pat. No. 5,461,318 to Borchert et al. (Oct. 24, 1995) which is amethod for detecting impedance discontinuities in a two-conductor cable.However, using conventional TDR techniques, this process involvessending service technicians to the ends of a physical line thenanalyzing the received signal via a local switch. As one can imagine,this entire process is time consuming, labor intensive and costly.

[0008] TDRs detect fault anomalies such as opens, shorts, bridged-tapsand wet sections. As these lines become longer the loss of the line ishigher and it becomes increasingly harder to detect these anomalies. Inmost cases it takes considerable training and practice to discriminatebetween these various anomalies. Often even the most experiencedtelephone technician must drive to other locations, disconnectingsections to resolve their problems.

[0009] One key factor in differentiating between a short, a wet sectionand bridged-tap is the size of the return trace. “Trace” is a graphicalrepresentation of the line voltage verse time. However since the size ofthis return trace is related to the cable type and distance, or in otherwords the cable loss (with the return trace decreasing in amplitude asthe distance increases), there is no existing method used to definitelyresolve these common cable plant problems. Loss with cable plants ofmixed cable types, makes detection for these faults even more complex.Detecting multiple faults at different lengths cannot be done on thesame trace, as the user must manually set the gain for only a particularrange of interest.

[0010] Another factor that masks the faults is a phenomenon calledback-scatter decay. As cables become longer this returning signalbecomes dominant over any detectable fault. Manual gain and offsetcontrols are often required to see faults at longer distances. The userof a traditional TDR have to manually change the gain on the TDR tracein order to see the faults.

[0011] Therefore, there currently exists a need for a system and methodto test the abnormalities of the copper pair lines that avoids thedisplaying problems and limitations associated with the currenttechniques. There also exists a need for a system and method to test theabnormalities of the copper pair lines that can aid in automaticallyshowing abnormalities within a predetermined observation range so as tomake the tracing and repair of copper pair lines for xDSL service moreefficient.

[0012] Time Varying Gain (“TVG”), a predetermined gain versus timerelationship, has been applied in side scanning sonar systems formapping the topography of a under water seabed. Acoustic tone bursts(pings) are transmitted through the water column toward a target areaand return from the target area are picked up by a receiver transducerand processed for display. Return signals may vary due to unknowns suchas temperature, salinity and clarity of the water column. If bottomreturns are involved, such as in side looking sonar systems, differentbottom types such as mud, sand or rock will return different signals.For instance, U.S. Pat. No. 4,198,702 to Clifford (Apr. 15, 1980)describes a time varying gain amplifier for a side scanning sonar systemhaving a predetermined gain versus time relationship. The gain issubstantially proportional to the square of the elapsed time measuredfrom the last sonar trace initiating trigger signal.

[0013] U.S. Pat. No. 5,392,257 to Gilmour (Feb. 21, 1995) furtherprovides a sonar receiver with a normalizing processor circuit tomodify/normalize the reflected signals to be displayed within the samerange by adjusting gain levels. Normalizing processor circuit means isprovided and is adapted to receive the signals reflected from unknownsin the water column and various bottom types, and the means is operableto generate an average error signal as a function of time. This errorsignal is applied to modify the output of the time varying gain circuit.

[0014] Adjusting gain levels is common in the art of data processing,and it has been applied to an optical time domain reflectometer (“OTDR”)in an optical measurement instrument. U.S. Pat. No. 4,893,006 to Wakaiet al. (Jan. 9, 1990) applies such a level adjusting function to an OTDRwhich works in conjunction with an optical fiber. The optical timedomain reflectometer tests a target optical fiber by sending an opticaltrace to the target optical fiber and detecting Fresnel reflection lightand backscattered light returning from the fiber. A level changing meanschanges the level of the electric signal corresponding to apredetermined location of observation range so as to avoid saturation ofthe electric signal in the amplifier. As another example, U.S. Pat. No.5,929,982 to Anderson (Jul. 27, 1999) applies such a level adjustingfunction (gain control) to an OTDR for optimizing the gain of an activeavalanche photo-diode (“APD”). Any system noise is compared to athreshold value for establishing the optimum bias for optimum gain ofthe APD thereby to increase the dynamic range of the OTDR.

[0015] However, the application of TVG to a TDR for telephone lines ofthe present invention is unique, and the application simplifies the useof TDR in testing for abnormalities in telephone and coaxial cables andenables the display of multiple faults at various cable lengths. Inaddition, detecting multiple faults at different lengths can be done onthe same trace automatically.

SUMMARY OF THE INVENTION

[0016] It is therefore a general object of the present invention toprovide an TDR with Time Varying Gain so as to display the abnormalitiesof a communication cable or the like in a predetermined observationrange.

[0017] Another object is to display a reflected trace in predeterminedamplitude, regardless of actual amplitude due to cable loss or cablelength for a particular given fault (open, short, bridge-tap or wetsection). In addition, multiple faults at various lengths can be seen ona single screen.

[0018] Another object is to provide a simple method and apparatus forinterpreting TDR traces which will then require less user training.

[0019] A further object is to eliminate backscatter slope and tohighlight faults.

[0020] A further object is to easily determine cable type by how wellthe back-scatter is matched. Further, if a user enters the incorrectwire type, some back-scatter slope will be present, and thus can becorrected. Accordingly, mixed cable types can be identified andcompensated for and the need for user intervention in selecting gainmanually is eliminated.

[0021] A further object is to provide an improved method and apparatusfor detecting a physical bridge tap and distinguishing the bridge tapfrom other types of cable fault.

[0022] The present invention involves a copper pair line abnormalitiestesting apparatus, procedure and protocol. First, parameters such aseach copper pair line's length, wire gauge, impedance, etc. are known,entered in the apparatus, or measured using known measuring techniques.Next, using a time varying gain domain reflectometer (TDR), a knownsignal or pulse is transmitted through the line; the CO or CPE can beused as the origin or starting point of the trace signal. The returnvoltage is measured, wherein impedance mismatches are identified by thecharacteristics of that return voltage. For example, with a time varyinggain TDR device having a display, impedance and wire gauge mismatchescan be identified visually by the presence of significant scope oramplitude changes in the graphical representation of the return voltage.The time varying gain TDR's graphical representations or trace, alongwith information from other measurements, or manually entered, isnormalized to eliminate the effects of the loose cable, namelyattenuation and backscatter. The normalization steps will then generategraphical representation indicative of the characteristics of theabnormalities of the copper pair line, wherein the abnormalities may beindividually graphically represented in a predetermined observationrange. The normalization steps are used to amplify the abnormalities inconjunction with the time interval of the TDR traces and at least onegain coefficient factor.

[0023] In accordance with one embodiment of the present invention, asystem for displaying abnormalities of a copper pair line comprising atleast one time varying gain time domain reflectometer (TDR) havingsupplying means for supplying at least one pulse of energy at a givenpulse width on to a base location of the copper pair line; receivingmeans for receiving the reflected pulse at the base location; measuringmeans for measuring the elapsed time from the transmission of the pulseto the receipt of the reflected pulse corresponding to the transmittedpulse; calculating means for calculating the distance from the baselocation to a abnormality causing the reflected pulse; piecewise gainingand biasing means for piecewise gaining biasing the reflected pulse ofvarious gains to create a first normalized reflected trace which matchthe reflected pulse of various gains within a predetermined observationrange and constitute as one smooth curve; a first time varying gaincircuit for amplifying said first normalized reflected trace accordingto a function of time to create a second normalized reflected trace soas to eliminate an exponential gain decay curve of a no-fault copperpair line with the same predetermined characteristic parameters fromsaid first normalized reflected trace to thereby obtain a secondnormalized reflected trace showing any amplified abnormalities; and adisplay for displaying at least one of the reflected trace, the firstand second normalized traces corresponding to a predeterminedobservation range. The abnormalities includes opens, shorts,bridged-taps and wet sections on the wire.

[0024] According to a further embodiment of the present invention, asystem as described further comprises a second time varying gain circuitfor amplifying said second normalized reflected trace according to afunction of time to create a third normalized reflected trace so as toamplify the abnormalities thereby to differentiate different types ofabnormalities.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are included to provide anunderstanding of the invention and constitute a part of thespecification.

[0026]FIG. 1 is a system block diagram of a preferred implementation andapplication of the present invention.

[0027]FIG. 2A is a system block diagram of the structural andoperational components of the preferred embodiments of the presentinvention.

[0028]FIG. 2B is a system block diagram of an alternative implementationfor the structural and operational components of the present invention.

[0029]FIG. 2C is a system block diagram of a further alternativeimplementation for the structural and operational components of thepresent invention.

[0030]FIG. 3 is a flow diagram of the general steps that comprise theprotocol for conducting the testing of abnormalities in a copper pairline according to the present invention; while the shaded boxesrepresenting traditional TDR SW routines.

[0031]FIG. 4 is a hardware gain and offset table.

[0032]FIG. 5A shows a graphical representation of three sets 12 bitreflected data from abnormalities of a copper pair line piecewisematched into one set of 16 bit data of the present invention.

[0033]FIG. 5B shows a graphical representation of the results of theFirst Normalization;

[0034]FIG. 6A shows a formula and a table of gain coefficient of theSecond Normalization according to Step 306 of FIG. 3.

[0035]FIG. 6B shows a graphical representation of the normalizationresults of the Second Normalization.

[0036]FIG. 7A shows a formula and a table of gain coefficient of the DCOffset of the Second Normalization according to Step 307 of FIG. 3.

[0037]FIG. 7B shows a graphical representation of the DC Offsetnormalization results of the Second Normalization.

[0038]FIG. 8A shows a formula and a table of gain coefficient of theThird Normalization according to Step 308 of FIG. 3.

[0039]FIG. 9A shows one implementation for a traditional TDR; and

[0040] FIGS. 9B-9D show preferred implementations and applications ofthe present invention according to FIG. 3.

[0041]FIG. 10 contrasts signals with and without the SecondNormalization. according to the present invention.

[0042]FIG. 11 shows the ability of the invention to detect the cabletype with an open fault.

[0043]FIG. 12 shows an open fault trace (after being processed throughthe First Normalization step).

[0044]FIG. 13 shows an open fault trace (after being processed throughthe Second Normalization step).

[0045]FIG. 14 shows a short fault trace (after being processed throughthe First Normalization step).

[0046]FIG. 15 shows a short fault trace (after being processed throughthe Second Normalization step).

[0047]FIG. 16 shows a bridge-tapped fault trace (after being processedthrough the First Normalization step).

[0048]FIG. 17 shows a bridge-tapped fault trace (after being processedthrough the Second Normalization step).

[0049]FIG. 18 shows traces of different types of faults expressed indifferent shapes (after being processed through the First Normalizationstep).

[0050]FIG. 19 shows traces of different types of faults expressed indifferent shapes (after being processed through the Second Normalizationstep).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0051] The present invention is based on the development of a system foranalyzing the structural and functional abnormalities of a copper pairline for xDSL service. By implementing the apparatus, methodology andprotocol of the present invention, one can in a step-by-step processprogressively test and trace the location and extent of theabnormalities without physically visiting the site.

[0052]FIG. 1 illustrates a system block diagram of the testingenvironment of the present invention. In particular, a conventionaltelephone system that would be tested using the present invention wouldincorporate a central office or exchange CO through which a plurality ofcopper pair lines 12 are connected and processed. Each copper pair linewould be composed of a cable loop pair 122 that has a CO end and a CPEend. Each cable loop pair terminates at a CPE end; a CPE is generallyembodied in the copper pair lines that connect into individual homes oroffices within proximity of the CO.

[0053] From either its CO end or the CPE end, a cable loop pair 122 istested using test equipment 20′ or 20″; test equipment 20′ is the systemimplemented at the CO end; while equipment 20″ is implemented at the CPEend. Applicants have found that the testing of the copper pair lines atthe CPE end generates more accurate predictions of the suitability ofthe copper pair lines for xDSL service due to the difficulties relatingto extended length attenuation, dispersions and interfering noise (i.e.,disturbers). Alternatively, test equipment 20″ can be implemented at across-box 14 of the copper pair lines. This would allow a user to testthe lines so as to be able to qualify each of the copper pair lines foran entire neighborhood or for all the offices in a building. Thisalternative, like the testing at the CPE end, has been found to producemore accurate test results. However, testing of the lines at the CO isequally valid as that done at either the CPE end or at a cross-box ofthe copper pair lines, although more challenging.

[0054] As shown in FIG. 2A, both test equipment 20′ and 20″ generallyconsist of components for, among others, (1) measuring the ambienttemperature of the copper pair line 201; (2) detecting the presence ofabnormalities 203; (3) detecting the presence of short circuits 205; (4)conducting a longitudinal balance test 207; (5) conducting time domainreflectometry 209 on the line; and (6) determining the presence ofwideband noise on the copper pair line 211. In a preferred embodiment ofthe present invention, each of the above components are implemented intoa single test instrument or system so as to make the conducting of thetests more efficient and portable. The structure and operation of thoseindividual components would be consistent with similar devices known inthe art. However, as one of skill in the art would understand, thesecomponents could also be implemented using a combination of known testdevices or systems that are either interconnected or simply appliedseparately in sequence.

[0055] For example, component 201 for measuring the temperature of thecopper pair line may consist of a conventional thermocouple device orother industrial temperature gauge. Applicants have found that, sincethe temperature of the copper pair line may vary along its length and asa result of environmental conditions at any point along the line, oneway of including temperature as a factor in the analysis is by using theambient temperature of the overall surrounding environment. For example,with copper pair lines that are suspended above the ground, thesurrounding air temperature is used.

[0056] Component 203 for detecting the presence of abnormalities, suchas load coils, build out capacitors, may consist of a conventionalsignal transceiver device capable of at least sweeping test signalsthrough a plurality of frequencies or “bins” by generating a signal ateach of the frequency bins and detecting a test signal resulting fromthe generated signal.

[0057] Short circuits in the copper pair line may be detected bycomponent 205 using a conventional ohmeter, multimeter or otherresistance measuring device designed for telecommunicationsapplications.

[0058] Longitudinal balance testing by component 207 would beaccomplished using any conventional voltage or current measuring devicecapable of measuring the common mode AC voltage or current, and thedifferential AC voltage or current in a copper pair line.

[0059] Time domain reflectometry would be implemented in component 209using a time domain reflectometer, using either a time domain or afrequency domain algorithm. To save having a separate component in thesystem for determining the presence of short circuits in the copper pairlines, the function of component 205 may also be performed by component209 since, as is known in the art, time domain reflectometry can be usedto determine the presence of short circuits in metallic paired cables.Noise in the copper pair lines would be measured by component 211 usingan analog receiver connected to an A/D converter so as to generate adigital representation of any noise signals it detects.

[0060] In testing for abnormalities on the line, component 209implemented as a TDR device is used to transmit pulse along the copperpair line. Return reflections of that known pulse which show theresulting attenuation of the pulse through a copper pair line areindicative of various conditions, including the presence or absence ofshort circuits, the presence or absence of open circuits, the presenceor absence of bridge taps, changes in the wire gauge of the line, thepresence of water, and the length of the copper pair line. The existenceand/or degree of existence of these conditions are in turn indicative ofthe line's capacity to handle xDSL service.

[0061] By tracking the time at which the trace is transmitted incomparison to the time at which a reflected trace is received by theTDR, the length of the copper pair line may be predicted based on theknown velocity of electromagnetic energy (i.e., the speed of light) andthe known velocity of propagation (VOP) through a copper wire of a knowngauge and having an ideal or known impedance.

[0062] In the general operation of the invention, the protocol forconducting the abnormality test, as illustrated in FIG. 3, involves thefollowing steps to be executed by the user or automatically via hardwareand/or software:

[0063] Step 301: A User selects cable length and cable type (suchparameters may further include line, impedance, the wire gauge,temperature of the line and cable construction type).

[0064] Step 302: Determining HW gain and DC offset data from a GainGauge Table as shown in FIG. 4; this corresponds with using the datafrom selecting cable length and cable type.

[0065] Step 303: Setting up clocks, relays, pal, FPGA samples per sweepand trace width.

[0066] Step 304: Sending and receiving data at HW settings specified inSteps 302 and 303, adjusting phase offset, and placing data in Rx array.

[0067] Step 305: First Normalization: comparing the reflected traces ofvarious gains with a predetermined observation range to set gain and DCoffset so as to bias the levels of the reflected pluses to be shown asone approximately smooth curve within the predetermined observationrange as shown in FIG. 5B.

[0068] Step 306: Second Normalization: Multiplying the array by theCable Attenuation Gain vs. Time per Wire-type gain constant according tothe formula shown in FIG. 6A so as to eliminate the exponentialbackscatter of a normal line of FIG. 5B, thereby obtaining a generallyhorizontal line with one or more abnormality waveforms as shown in FIG.6B.

[0069] Step 307: Removing average DC offset from FIG. 7B so as to levelthe amplitude of the line in FIG. 7B to 0 except at the one or moreabnormality waveforms. Step 308: Third Normalization: Multiplying thearray by the Trace Attenuation Gain vs. Time per Wire-type gain constantaccording to the formula shown in FIG. 8A so as to amplify theabnormality waveforms and to better distinguish different types ofabnormalities.

[0070] Step 309: Displaying the digital data obtained after the ThirdNormalization.

[0071] In contrast, the protocol for conducting the abnormality test inthe prior art only involves the steps illustrated in the shaded boxes301, 302, 304, 305 and 310 of FIG. 3, and they are conducted by atechnician manually adjusting the equipment. In determining whether anyabnormalities are present on the copper pair line, one implementation ofthe prior art would be to generate an AC voltage into the copper pairline at some known level and their frequencies range from 250 to 3000Hz, measure the return current, and then plot the resulting data on anamplitude vs. cable length graph. The presence of abnormalities isgenerally represented by the occurrence of changes in the slope whereeach bump on the plot indicates some type of abnormality in a specificlocation of the line. As mentioned, a technician manually checks thegain table to adjust the three sets of 12 bit data lines in FIG. 5A intoone set of 16 bit data line in FIG. 5B.

[0072] In terms of the physical embodiment of a traditional TDR, asshown in FIG. 9A, all TDRs start with a pulse generator 1 whichtransmits a trace of energy onto the cable and receiving any reflectedtraces at a base location. For balanced lines as in the telephonesystem, the trace differentially drives the line with a line driver 2through impedance matching resistors 3. This differential trace istransmitted into the line under test. Any faults will cause a reflectedwave that will arrive at the differential receiver 5 at a later time.The adjustable gain controlled amplifier 6 attenuates or amplifies thereturn signal before it can be digitized by the AID converter 7. Thesedigitized samples are read into a microprocessor 9 and displayed foruser interpretation. The distance to the discontinuity is calculated bymeasuring the elapsed time between the transmitted and received pulses.All digital timing is controlled with some sort of synchronous digitaltiming generator 4. A trace is created on a display screen showing thetransmitted and reflected traces, by taking a plurality of horizontalsamples along the copper pair line, and calculating a vertical value foreach horizontal sample taken. Each horizontal sample is then convertedto digital form and displayed on the screen.

[0073] In the present invention, as shown in FIG. 9B, an ExponentialVoltage Generator 8 is employed to implement solutions I, II toaccomplish the first two unique normalization steps (steps 305-306 ofFIG. 3) so as to bias the levels of the reflected pulses of variousintensities, integrate them into an approximately smooth curve shown inFIG. 5B, and then to obtain a normalized waveform showing one or moreabnormality bumps.

[0074] To realize a TDR of the above-described embodiment with a timevarying gain proportional to the abnormality of a cable type, at leastthree solutions (via hardware, post-processing software or combinationof HW & SW) are available and described below:

[0075] Solution I: Hardware Method #1 (See FIG. 9B)

[0076] With this method the “pulse gate” drives the Exponential VoltageGenerator 8 which dynamically changes the gain of the voltage controlledadjustable gain amp 6 in a time varying manner. This method appears tobe the most straightforward approach; however, matching the amplifiergain to the exponential decaying voltage in a repeatable fashion israther difficult.

[0077] Solution II: Hardware Method #2 (See FIG. 9C)

[0078] With this method the “pulse gate” drives the Exponential VoltageGenerator 8 which dynamically changes the gain of the A/D converter 7 bydynamically varying the reference voltage of converter 7 in a timevarying manner. This method is easier then method #1 as the exponentialdecay of a simple RC circuit is nearly the decay required by the A/Dconverter reference voltage input. However as different cable types areto be tested, each type would require a different corresponding decay.

[0079] Solution III: Software Method (See FIG. 9D)

[0080] This method does not require the Exponential Voltage Generator 8,a voltage controlled adjustable gain amp 6, or a dynamically adjustablereference voltage for the A/D converter 7. Instead, the method requiresdigitized samples or “words” and a post process to divide the words by apredetermined table of cable loss for each cable type. The advantage ofthis method is less hardware as well as reliable control of the timevarying gain.

[0081] In a preferred implementation of the present invention, the TDRincorporates the hardware and software necessary for determining theabnormality of a line based on both calculating the abnormality fromcomplex signal analysis. Applicants have found that, under certainconditions, one method has distinct advantages over the other.Therefore, in order to maximize accuracy and efficiency, the presentinvention uses either method depending on the circumstances and on thedesires/requirements of the user.

[0082] Through a processor, the reflected pulses are transformed suchthat they were displayed on the same observation range. However, Thoselines can then normalized by a further data processing device or programto determine what characteristics of the copper pair line theyrepresent.

[0083] The First Normalization of Step 305 is accomplished, in oneembodiment, via the controller circuit, which includes adata/mathematical processor device or programs designed to separate asignal or mathematical representation of a reflected trace into its basecomponent waveforms, by comparing the reflected traces of variousfrequencies with a set of gain & DC offset references so as to bias thelevels of the reflected pluses of various intensities to be matched andshown as one approximately smooth curve shown in FIG. 5B.

[0084] The equation for the First Normalization (t)=1^(st) segment RawData/HWG1−Offset 1+2^(nd) segment Raw Data/HWG2−Offset 2+3^(rd) segmentRaw Data/HWG3−Offset 3. The inputted traces originates from the testingconducted using the TDR component 209.

[0085] The Second Normalization of Step 306 is accomplished, in oneembodiment, by the multiplication of the signal from Step 305 givenapproximately by the Gain2=2.718^ (t/Kg2), where t is time of sample innS and Kg is the gain coefficient corresponding to the wire gauge andpulse width shown in the table of FIG. 6A. FIG. 6B illustrates the gaincurve for a time varying gain TDR after the Second Normalization. Thevertical axis is the amplitude of the signal in volts and the horizontalaxis is the length in Kft of the copper pair wire to be tested forabnormalities. As shown in FIG. 6B, the gain remains relative constantuntil it approaches to the location of the abnormality.

[0086]FIG. 10 contrasts the signal with and without the SecondNormalization. After the Second Normalization, the abnormality is‘amplified’ into a platinum in line 2, which is much more clearer thanthe insignificant slope changes in line 1.

[0087] The DC offset removing step in 307 offsets a direct currentportion form the signal. Effectively, the offset in the range of x-yvolts is filtered from the waveforms resulting in FIG. 7B, 2^(nd)Normalization DCO(t)=2^(nd) Normalization−Offset_(—)2^(nd)_Norm.

[0088] The Third Normalization of Step 308 is accomplished, in oneembodiment, by the multiplication of the signal from Step 307 givenapproximately by the 3rd Normalization (t)=2^(nd) NormalizationDCO*Gain3; Gain3=2.718^ (t/Kg3), where t is time of sample (tracefrequency) in nS and Kg is the gain coefficient corresponding to thewire gauge and pulse width shown in the table of FIG. 8A. FIG. 8Billustrates the gain curve for a time varying gain TDR after the SecondNormalization. The vertical axis is the amplitude of the signal aftermathematical manipulation and the horizontal axis is the length in Kft(as compensated for VOP) of the copper pair wire to be tested forabnormalities. As shown in FIG. 8B, the gain remains relatively constantuntil it approaches to the location of the abnormality.

[0089] The output from Step 305 can be mathematically manipulated,either manually or within the controller circuit 213, to output agraphical representation of the signal characteristics of the copperpair line, such as the formula B, C and D.

[0090] The gain modified by the normalization process is characterizedby the gain coefficient factor, Kg. The numerical variation in Kgadjusts gains to the final multiplied signal. As noted above, the wiregauge, temperature and cable construction type are parameters thataffect Kg. The inclusion of these parameters in the calculations willimprove the accuracy of the analysis. However, Applicants have foundthat the lack of actual values for these parameters does not prevent theanalysis from being conducted nor from generating valid data, asestimates of these parameters can be used in the analysis.

[0091]FIGS. 6A, 7A and 8A show that the gain coefficient Kg generallyincreases with the increase of the pulse width, but it generallydecreases with the increase of the wire gauge, which is a series ofexperimental figures. For example, if the wire gauge is 19 and the pulsewidth is 250 nS, then Kg on the formula needs to be set at 2,489.

[0092] As an output trace, the controller circuit 213 will convert thecharacteristic data results generated by the processor 213 a and displaythem on the display 215. Depending on the requirements of the user, thedata results are presented as either raw mathematical or formula data,graphically represented as equivalent circuit diagrams of the copperpair line's characteristics, and/or graphically represented as part ofan overall diagram on the display 215 of the plant map of one or morecopper pair lines connected to or originating from a specific CO orcross-box.

[0093] With respect to the cable type choosing step 301, the user simplyinputs the data on a cable to be tested into the system. If the userinputs parameters different from those of the cable actually beingtested, the display will deviate from a horizontal level as FIG. 11.FIG. 11 shows the ability of the invention to detect the cable type withan open fault.

[0094] Detailed analyses of the return trace waveforms will reveal manyof the characteristics of the line being tested. With lines that havefew or no unusual configurations (i.e., no bridge taps, no change inwire gauge, no physical damage), those characteristics can easily bemeasured and quantified since specific return trace waveforms will beindicative of certain characteristics, as known in the art. However,with lines that do have complex configurations, complex trace analyseswould have to be conducted on their return trace waveforms, usingalgorithms and mathematical processes to identify and/or model theindividual components of the measured waveform. The measurements andcalculations as discussed below employ unique algorithms to level theamplitude of reflected traces within a specific range to showabnormalities to be compared with an abnormalities data bank for themost likely impairments. In particular, the candidates with the largestarea and those that were found in the greatest number of traces. Thoseabnormalities not meeting that criteria are eliminated as being minorperturbations that should not be counted as true impairments.

[0095]FIGS. 12, 14 and 16 show an open, short and bridge-tapped faultrespectively (after the First Normalization). FIGS. 13, 15 and 17 showthose faults after the Second Normalization. To contrast the differentshapes expressed by different types of faults, three output lines areshown on FIGS. 18 (after the First Normalization) and 19 (after theSecond Normalization). FIG. 19 also evidences one advantage of thepresent invention, reducing the back-scattered effect. Further more,FIGS. 13, 15, 17 and 19 contrast the signals in FIGS. 12, 14, 16 and 18with the effect of the Second Normalization. After the SecondNormalization, the abnormality is ‘amplified’ into much more clearerlines.

[0096] If the reflected trace were to return with an time varyingamplification near the shape and level of the original trace or a smoothexponent graphical representation of the original trace with a gradualdrop in amplitude, this would indicate that little or no change in theimpedance along the length of the line was encountered, therebyindicating no substantial faults or damage present. On the other hand, areflected trace with a substantial slope change would show a change inthe impedance of the line that then indicates that a abnormality alongthe line, such as damage to the copper cables, is present resulting in apartial reflection of the original trace. Prominent “short” in thegraphical representation would indicate the presence of short circuits(e.g., drop in impedance), while prominent “positive bump or slopechange” in the graphical representation would indicate an open circuitcondition (e.g., increase in impedance). Bridged taps, water, poorsplices or gauge changes are all different forms of either “shorts” or“opens” in the line.

[0097] The time difference related to the partial reflection would beindicative of the distance between the starting point and the locationof the abnormality. In addition to the type of analysis discussed above,other characteristics of the return trace (i.e., whether the returntrace is in phase or out of phase, whether the return trace the samepolarity or the inverse of the original) may be indicative of otherconditions of the line. However, as one of skill in the art willunderstand, the information one may derive from these characteristicswill vary depending on the construction of and algorithm used by the TDRimplemented in the system of the present invention.

[0098] For example, a custom-programmed abnormality modeling softwaresimulates the equivalent abnormality of the line would then be used toanalyze any to-be-tested copper pair lines. The characteristics of theabnormalities of the copper pair line are estimated indirectly bycomparing the reflected trace with a library of already knownabnormalities; in particular, the comparison is between the compleximpedance represented by the return trace signal and known pluses thatrepresent known abnormalities. The implementation involves the use of amemory or data bank connected to or accessible by controller circuit213. In using the data bank, the controller circuit 213 uses acomparison device or algorithm to compare the known in the data bankwith the reflected trace from the TDR device 209. In essence, thecomparison device would incorporate a system for searching the mostrelevant known abnormalities and comparing the characteristics of onlythose known abnormalities with the reflected trace. One implementationfor the bank of known abnormalities uses a plurality of known copperpair lines. That bank of known wires can be supplemented withcustom-designed copper pair wires derived from research,experimentation, simulation and/or field data.

[0099] In one implementation of the invention as shown in FIG. 2A,components 201-211 are incorporated into a testing equipment 20′, 20″implemented as a single, dedicated testing device that includes acontroller circuit 213 electrically connected to each of the components201-211. The control circuit 213 includes a microprocessor, a digitalsignal processor (DSP) or other data processing device for receivinginput data from each of the components 201-211, processing the inputdata so as to generate characteristic data on the copper pair line beingtested, and outputting the characteristic data in a form that a userwould understand. In particular, that testing device further includes adisplay device 215 or other know output mechanism through which thecontrol circuit would display the characteristic data in arepresentative and user-understandable fashion.

[0100] Components 201-211 in this implementation embody either separatetest circuit devices that generate data that is then inputted into thecontroller circuit 213, or simply the testing elements or probes forperforming their respective functions. In that regard, controllercircuit 213 is implemented with the conventional hardware/software tofirst generate/output test signals (where appropriate), and thenreceive/interpret input signals from the test elements or probes. Evenmore, with functions such as load coil testing, longitudinal balancetesting and time domain reflectometry, as noted above, components201-211 may be implemented as a single testing element or probe 219 (SeeFIG. 2C) that is designed to output as well as receive the appropriatesignals for conducting the various tests, thereby minimizing the numberof different components needed. In such an implementation, theindividual components 201-211 would be furthered embodied in softwareprogrammed into the controller circuit 213 so as to control the testingelement or probe 219.

[0101] Alternatively, as illustrated in FIG. 2B, the controller circuit213 can be implemented as a remotely-connected computer (e.g., desktopcomputer, laptop computer, mainframe, electronic controller) thatcommunicates with the components 201-211 via hardwire cable, RFcommunication, infrared communication, laser communication or any otherinput/output data transfer device that one of skill in the art woulddeem appropriate under the circumstances. The components 201-211 arethen each implemented as stand-alone instruments connected via acorresponding input/output data transfer device 217 so as to communicatedata to/from the controller circuit 213. The components 201-211 may alsobe implemented as the testing elements or probes for performing theirrespective functions. Again, with functions such as load coil testing,longitudinal balance testing and time domain reflectometry, the sametesting element or probe 219 may be used to perform a plurality ofdifferent tests. As with the prior implementation discussed above, thecontroller circuit 213 would then have to implement the necessaryhardware and software to communicate and/or control this implementationof the components 201-211.

[0102] As one of skill in the art would understand, the data transferdevice 217 may be (a) a plurality of communication devices eachconnected to one of the components 201-211, if separate components, andthus independently connected to the control circuit 213; (b) anintegrated communication device connected to transfer data signals toand from the components 201-211 and to transfer data to and from thecontrol circuit 213; (c) an integrated communication device connected totransfer data signals to and from the testing element or probe 219 andto transfer data to and from the control circuit 213; or (d) aninput/output circuit device integral to the controller circuit 213(i.e., a USB device) such that each of the components or a singletesting element or probe are connected directly to or communicatedirectly with the controller circuit 213.

[0103] As an even further alternative, the invention may be implementedmanually by the use of conventional implementations of each of thecomponents 201-211 that are used in sequence in accordance with thetesting protocol of the present invention, as will be explained furtherhereinbelow. A user would take the data outputted by each of theseparate components, and input them into a data processing device (e.g.,the implementation of the controller circuit 213) in order to generatethe desired data. This data may then be filtered through a set ofpass/fail criteria, being summarized to single pass/fail result,allowing even a very unskilled person to determine a line fit for DSLservice with a high degree of accuracy and confidence.

[0104] The present invention is not to be considered limited in scope bythe preferred embodiments described in the specification. Additionaladvantages and modifications, which will readily occur to those skilledin the art from consideration of the specification and practice of theinvention, are intended to be within the scope and sprit of thefollowing claims.

What is claimed:
 1. A method for providing a time varying gain time domain reflectometer (TDR) to display abnormalities of a copper pair line, comprising the steps of: providing a time varying gain TDR; transmitting from the TDR at least one pulse at a given pulse width into the copper pair line; receiving a reflected pulse from the copper pair line; measuring the elapsed time from the transmission of the pulse to the receipt of the reflected pulse corresponding to said transmitted pulse; calculating the distance from the base location to an abnormality causing the reflected pulse; piecewise gaining and biasing the reflected pulse of various gains to create a first normalized reflected trace which match the reflected traces within a predetermined observation range and thereby constitute a total smooth curve; amplifying said first normalized reflected trace according to a function of time to create a second normalized reflected trace so as to eliminate an exponential gain decay curve of a no-fault copper pair line with the same predetermined characteristic parameters from said first normalized reflected trace to thereby obtain a second normalized reflected trace showing any amplified abnormalities; and displaying at least one of the reflected trace, the first and second normalized traces corresponding to a predetermined observation range.
 2. A method according to claim 1, whereby the step of amplifying said first normalized reflected trace includes a step of amplifying said first normalized reflected trace exponentially corresponding to the time interval.
 3. A method according to claim 1, whereby the step of amplifying said first normalized reflected trace includes a step of amplifying said first normalized reflected trace with a gain corresponding substantially to the time interval, and a step of dividing over a first predetermined gain coefficient factor, whereby the first predetermined gain coefficient factor is determined according to at least one of the characteristic parameters including a wire gauge, length and temperature of the copper pair line.
 4. A method according to claim 3, whereby the step of amplifying said first normalized reflected trace further includes a step of multiplying said first normalized reflected trace by a factor of 2.718.
 5. A method according to claim 1 further comprising a step of offsetting a direct current portion from said second normalized reflected trace.
 6. A method according to claim 5, whereby the step of offsetting said second normalized reflected trace includes a step of offsetting said second normalized reflected trace with a DC offsetting coefficient factor, whereby the DC offsetting coefficient factor is determined according to at least one of the characteristic parameters including a wire gauge, length and temperature of the copper pair line.
 7. A method according to claim 1 further comprising a step of amplifying said second normalized reflected trace according to a function of time so as to create a third normalized reflected trace to further amplify the amplified abnormalities.
 8. A method according to claim 7, whereby the step of amplifying said second normalized reflected trace is to amplify said second normalized reflected trace exponentially corresponding to the pulse width.
 9. A method according to claim 7, whereby the step of amplifying said second normalized reflected trace includes a step of amplifying said second normalized reflected trace with a gain corresponding substantially to the pulse width, and a step of dividing over a second predetermined gain coefficient factor, whereby the second predetermined gain coefficient factor is determined according to at least one of the characteristic parameters including a wire gauge, length and temperature of the copper pair line.
 10. A method according to claim 9, whereby the step of amplifying said second normalized reflected trace further includes a step of multiplying said second normalized reflected trace by a factor of 2.718.
 11. A method according to claim 9, whereby the amplitude of said at least one trace of energy is proportional to an expected reflected pause from the copper pair line.
 12. A method according to claim 1, whereby the abnormalities include opens, shorts, bridged-taps and wet section on the line.
 13. A method according to claim 1, wherein the step of determining the cable gauge includes the automatic steps of: (a) taking a predetermined number of horizontal samples along the cable to fill a horizontal length of a display screen; (b) determining a value for a baseline ahead of the transmitted trace waveform; (c) determining a preliminary initial value of the first horizontal sample on the following side of the transmitted trace waveform; (d) selecting a decay slope from a plurality of predetermined decay slopes, based upon the preliminary initial value; and (e) selecting a cable gauge by matching said decay slope one of a plurality of decay slopes in a look up table having different decay slopes based upon a variety of initial and wire gauges for various trace widths.
 14. A method according to claim 1 further comprising the step of: determining and discriminating the characteristics of the abnormalities on the wire by at least one of slope changes and widths of traces.
 15. A method according to claim 14, wherein the step of determining and discriminating the characteristics of abnormalities on the wire further includes performing an abnormalities modeling analysis.
 16. A method according to claim 14, wherein the step of determining and discriminating the characteristics of abnormalities on the wire includes comparing the normalized pluses with a plurality of normalized pluses associated with predetermined abnormalities.
 17. A system for displaying abnormalities of a copper pair line, comprising at least one time varying gain time domain reflectometer (TDR) comprising: supplying means for supplying at least one pulse of energy at a given pulse width on to a base location of the copper pair line; receiving means for receiving the reflected pulse at the base location; measuring means for measuring the elapsed time from the transmission of the pulse to the receipt of the reflected pulse corresponding to the transmitted pulse; calculating means for calculating the distance from the base location to a abnormality causing the reflected pulse; piecewise gaining and biasing means for piecewise gaining biasing the reflected pulse of various gains to create a first normalized reflected trace which match the reflected pulse of various gains within a predetermined observation range and constitute as one smooth curve; a first time varying gain circuit for amplifying said first normalized reflected trace according to a function of time to create a second normalized reflected trace so as to eliminate an exponential gain decay curve of a no-fault copper pair line with the same predetermined characteristic parameters from said first normalized reflected trace to thereby obtain a second normalized reflected trace showing any amplified abnormalities; and a display for displaying at least one of the reflected trace, the first and second normalized traces corresponding to a predetermined observation range.
 18. A system according to claim 17, further comprising: a second time varying gain circuit for amplifying said second normalized reflected trace according to a function of time to create a third normalized reflected trace so as to amplify the abnormalities thereby to differentiate different types of abnormalities.
 19. A system for displaying abnormalities of a copper pair line, comprising: supplying means for supplying at least one pulse of energy at a given pulse width on to a base location of the copper pair line; receiving means for receiving the reflected pulse at the base location; measuring means for measuring the elapsed time from the transmission of the pulse to the receipt of the reflected pulse corresponding to said transmitted pulse; calculating means for calculating the distance from the base location to a abnormality causing the reflected pulse; piecewise gaining and biasing means for piecewise gaining biasing the reflected pulse of various gains to create a first normalized reflected trace which match the reflected pulse of various gains within a predetermined observation range and constitute as one smooth curve; a first time varying gain circuit for amplifying said first normalized reflected trace according to a function of time to create a second normalized reflected trace so as to eliminate an exponential gain decay curve of a no-fault copper pair line with the same predetermined characteristic parameters from said first normalized reflected trace to thereby obtain a second normalized reflected trace showing any amplified abnormalities; and a display for displaying at least one of the reflected trace, the first and second normalized traces corresponding to a predetermined observation range.
 20. A system according to claim 19, further comprising: a second time varying gain circuit for amplifying said second normalized reflected trace according to a function of time to create a third normalized reflected trace so as to amplify the abnormalities thereby to differentiate different types of abnormalities. 